The present invention relates to a method for loading and exchanging the rollers of the printing units of a printing machine and to a device for working the method.
Generally, a printing machine comprises a plurality of printing units arranged one after another in the case of a flexographic printing machine in line, for example. In this kind of machines, each printing unit comprises a plate cylinder on which the ink is deposited by an engraved roller, commonly called “anilox cylinder” by workers in the art. This engraved roller is supplied with ink, in well known manner, either by means of a doctor blade chamber or an inking roller associated with an ink pan. The plate cylinder prints directly, by contact, the matter to be printed, by using a pressure roller applying the matter to be printed against the plate cylinder. The engraved rollers include, at their cirucumference, cells intended to retain the ink having to be deposited on the printing plate of the plate cylinder. The volume per surface unit of these cells varies according to the jobs to be performed. Thus, the use of different engraved rollers for each specific job to be performed will be necessary. That means that these engraved rollers have to be exchanged according to the desired printing quality, an engraved roller used for a print including large “tint blocks”, i.e. large surfaces uniformly supplied with ink, will not be appropriate for fine prints not including large “tint blocks”.
Exchange solutions of an engraved roller have already been proposed. One of these solutions is described in patent CH 686 355 A5. In this patent, the exchange of the engraved roller is carried out by means of a carriage comprising engraved roller supports. In order to exchange an engraved roller, this carriage is laterally introduced between two printing units and the engraved roller, having been previously withdrawn from its bearings, is brought to the level of the engraved roller supports of the carriage. The carriage can be built in various ways and include either a lifting system with cross-pieces or actuators acting directly on the vertical movement of the engraved roller supports. The engraved roller having been brought to the level of the engraved roller supports, the latter are moved to the top so as to come into contact with the engraved roller in order to support it. The carriage is then laterally withdrawn from between the printing units and brought, outside the machine, towards a processing station where the used engraved roller can be removed and replaced by a new engraved roller. The replacement of the engraved roller having been carried out, the carriage is again introduced between the printing units and the new engraved roller is placed by repeating, in the reverse order, the same operations as for its withdrawal from the printing unit. Another solution, substantially identical to that described herebefore, is described in European patent EP 0 401 636 B1.
The two above-mentioned solutions present the drawback that the operator is obliged to get in between the printing units for exchanging the engraved rollers, thus requiring his particular attention as regards his security. Another drawback lies in the fact that the exchange of the engraved rollers is a relatively long operation, during which the machine is at standstill so that its productivity is reduced accordingly.